1. Field of the Invention
This invention concerns devices for use in repairing aneurysms, especially of the abdominal aorta.
2. Brief Discussion of the Related Art
An aneurysm occurs when an arterial wall becomes weakened to the extent that the weakened section balloons under pressure from the blood flowing through the artery. An aneurysm can lead to fatality if it ruptures causing rapid loss of blood.
An aortic aneurysm can be repaired by an endovascular repair procedure, in which a graft is inserted into the aneurysm via the femoral artery effectively to take the blood flow and to isolate the aneurysm. There are three forms of aortic endograft in current usage. The first is a straight stented tube graft. This may be used when there are adequate proximal and distal aortic necks for graft implantation. The tube may be stented at each end for support and to provide pins or hooks for embedding into the arterial wall to secure the tube in place. Alternatively, the tube may be stented throughout its length, such as by means of a metal wire stent. This form of endograft is used most commonly to repair aneurysms of the thoracic aorta.
An alternative construction of graft is a bifurcated tube for use in a patient with an abdominal aortic aneurysm where there is inadequate distal aortic neck but appropriate iliac artery configurations.
The third variation of endovascular graft is an aortouniliac graft, in which the tube extends from the proximal aortic neck into one of the iliac arteries. With this configuration an extraanatomic femofemoral bypass graft with a contralateral occlusion device in the common iliac artery is required. This device may be used when significant aneurismal disease is present in the contralateral iliac artery, precluding successful bifurcated graft placement.
A problem with such grafts is that over time, even over a period of two years, the graft can slip due to wear and tear on the stents, the effect of pulsatile blood flow through the tube and changes in the morphology of the arteries. The blood flow effect can be exaggerated as the graft slips and is able to bend and flex. Thus over time the integrity of the graft and isolation of the aneurysm can be compromised.
Another problem with stented grafts is that the twisting or flexing of the graft can cause fatigue in the metal stent. Such fatigue leads to fracturing of the stent wire and the resultant wire ends can pierce the graft material. Holes in the graft material mean that the aneurysm is no longer isolated from the blood flow.
Such grafts are generally used in a planned manner with the graft being selected for a specific patient according to precise pre-operative measurement of the aorta and adjacent arteries. Therefore, such grafts are not readily suited for use in repairing a ruptured aneurysm, where an emergency procedure is required simply to prevent death.